The invention relates to a concrete mixer, and more particularly, to a concrete mixer employing vibrations to aid the mixing action.
A mixer of this type is known from U.S. Pat. No. 4,148,588. The rotatable drum for producing concrete which is found in this mixer has supply openings on its top, into which a fluid charge containing the concrete ingredients is introduced. The mixing process is improved by means of vibrators, which are each excited via unbalanced mass motors on a vibrating plate. Because of the disposition of the oscillating plate and because of the unbalanced mass motors, the mixer is expensive in terms of its structure. Its energy requirement furthermore appears to be relatively high.
The same is true of a mixer such as that known from German laid open application 2,425,158. The mixer is filled from the top and the finished, mixed product is removed at the bottom. From the bottom, a shaft which is driven for rotation protrudes into the drum. The shaft has elastic laminations as mixing elements. A number of shaker elements are also disposed in the vicinity of the interior drum wall. The part of each shaker element which acts directly upon the material being mixed comprises a plate which is adapted to the curvature of the mixing vessel wall and which overlaps a corresponding opening in the wall from the inside of the mixer. This plate is connected with the wall via an elastic intermediate wall, which covers the opening and is simultaneously intended to prevent the transmission of the shaking action to the vessel wall. Each plate has its own drive means in the form of an electric unbalanced mass shaker, which is located outside the mixing vessel. This known mixer is extremely expensive structurally because of the required openings in the drum wall, the precise adaptation of the shaker plate shape and the associated seals, as well as the need for a plurality of separate unbalanced mass shaker elements. It is doubtful that the described effect of the shaking action on the material being mixed is in fact attained. Further disadvantages are the significant tendency to breaking down, because the elastic seal is encountered by the material being mixed and becomes corroded with time; also, transmission of the shaking action to the drum cannot be prevented by the seal, so that the mixing vessel and its bearing, like the mixer shaft, are subjected to increased wear. Driving a plurality of shaker elements (four in the exemplary embodiment) also necessitates a relatively high expenditure of additional energy.